1. Technical Field
The present invention relates to relates to a liquid crystal device and a projector.
2. Related Art
In existing liquid crystal display apparatuses such as twisted nematic (TN) liquid crystal display apparatuses, electrodes disposed on a pair of substrates between which a liquid crystal is sealed apply an electric field in a direction substantially vertical to a surface of the substrates to control an alignment of liquid crystal molecules to modulate a light transmittance. Recently, a method in which electrodes disposed on one of the pair of substrates apply an electric field in a direction substantially parallel to a surface of the one substrate has been available. This liquid crystal display mode is referred to as a lateral electric field or in-plane switching (IPS) mode.
As with a vertical alignment (VA) mode, the lateral electric field mode is adopted in liquid crystal panels for direct-view large television screens, and provides in-plane switching of a director of the liquid crystal molecules, thus achieving the advantage of low viewing-angle dependence. Liquid crystal light valves of projectors as well as direct-vision display apparatuses, including lateral-electric-field liquid crystal panels, have been proposed. In the lateral electric field mode, in particular, thin film transistors (hereinafter abbreviated as TFTs) are used as pixel switching elements, thereby achieving the advantage of no need for common electrodes on a counter substrate.
FIG. 15 is a plan view of a pixel, showing an example of a lateral-electric-field liquid crystal device of the related art. In the liquid crystal device of the related art, as shown in FIG. 15, a plurality of data lines 101 and a plurality of scanning lines 102 are orthogonal to each other. A TFT 103 is disposed near an intersection of each of the data lines 101 and each of the scanning lines 102. A comb-shaped pixel electrode 104 and a comb-shaped common electrode 105 are disposed so as to be interdigitated with each other, and the pixel electrode 104 is connected to the TFT 103 through a contact hole 106. The common electrode 105 is electrically connected to a common electrode line 108 through a contact hole 107. With the above structure, a potential corresponding to an image signal is applied to the pixel electrode 104 from the data line 101 via the TFT 103, and a potential common to pixels is applied to the common electrode 105 from the common electrode line 108 via the contact hole 107. As used herein, electrode portions extending in parallel to each other in each comb-shaped electrode are referred to as “strip-shaped electrode portions”, and a portion for connecting the strip-shaped electrode portions is referred to as a “joint portion”. The electrodes 104 and 105 include joint portions 104b and 105b arranged along the data lines 101, and strip-shaped electrode portions 104a and 105a, respectively. The strip-shaped electrode portions 104a and the strip-shaped electrode portions 105a are alternately disposed so as to face each other, and a lateral electric field is generated between the strip-shaped electrode portions 104a and the strip-shaped electrode portions 105a. A liquid crystal is driven by the lateral electric field (see, for example, JP-A-9-258242).
JP-A-9-258242 noted above describes that bus lines such as data lines and scanning lines and comb-shaped electrodes are defined on different layers so that the bus lines and the comb-shaped electrodes can overlap each other in plan view, thereby increasing the aperture ratio. However, the structure described in JP-A-9-258242 has a problem. While a uniform lateral electric field is generated in a liquid crystal layer at a position where the strip-shaped electrode portions of each of the electrodes face each other (e.g., a position surrounded by a circle A in FIG. 15) to provide normal display, it is difficult to generate a lateral electric field immediately above the joint portion of the electrode that partially overlaps the bus lines, resulting in a low light transmittance at the corresponding position during bright display. Further, a lateral electric field with various directions is generated in at a position where the strip-shaped electrode portions and the joint portion face each other (e.g., a position surrounded by a circle B in FIG. 15) to cause alignment disorder of the liquid crystal, resulting in a low light transmittance at the corresponding position during bright display. Therefore, the surface area can substantially contribute to the display is reduced and a sufficient aperture ratio of the pixels is not obtained, thus preventing bright display. The low-aperture-ratio problem becomes more serious in particular for liquid crystal devices with a smaller pixel pitch such as liquid crystal devices used for liquid crystal light valves.